Prediction of plane-strain specimen geometry to efficiently obtain a forming limit diagram by Marciniak test

2018 ◽  
Vol 25 (5) ◽  
pp. 539-545 ◽  
Author(s):  
Qing-bao Yang ◽  
Jun-ying Min ◽  
John E. Carsley ◽  
Yuan-yuan Wen ◽  
Bernd Kuhlenkötter ◽  
...  
Keyword(s):  
Plane Strain ◽  
Forming Limit Diagram ◽  
Specimen Geometry ◽  
Forming Limit ◽  
Marciniak Test

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

2012 ◽  
Vol 504-506 ◽  
pp. 71-76 ◽  
Author(s):  
Alexandra Werber ◽  
Mathias Liewald ◽  
Winfried Nester ◽  
Martin Grünbaum ◽  
Klaus Wiegand ◽  
...  
Keyword(s):  
Plane Strain ◽  
Biaxial Loading ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Linear Strain ◽  
Forming Limits ◽  
Systematic Analysis ◽  
Measurement Systems ◽  
Non Linear ◽  
Strain Paths

In order to evaluate the formability of sheet materials forming limit diagrams (FLD) are recorded which represent the values of major and minor strain when necking occurs. FLDs are recorded based on the assumption that exclusively linear strain paths occur. In real forming parts, however, particularly in those with complex shapes, predominantly non-linear strain paths occur which reduce the accuracy of the failure prediction according to a conventional FLD. For this reason forming limits after loading with non-linear strain paths have to be investigated. In this contribution a systematic analysis of the forming limits of a conventional AA6014 alloy after loading with non-linear strain paths is presented. This material is pre-stretched in uniaxial, plane strain and biaxial direction up to several levels before performing Nakajima experiments in order to determine FLDs. During the pre-stretching process as well as during the Nakajima experiment the strain distribution can be measured online very precisely with the optical deformation measurement systems GOM Aramis or VIALUX. The gained curves are compared to the FLD of the as-received material. The results prove a significant influence of the pre-stretching condition on the forming limits of the used aluminum alloy. For a low pre-stretching in uniaxial as well as in biaxial direction the FLDs show a slightly reduced formability while after higher pre-stretching levels the forming limit can be improved such as for biaxial loading after uniaxial pre-stretching. The formability after pre-stretching in plane strain direction was changed. Also, a shift of the FLD depending on the direction of pre-stretching can be observed.

Investigation of the Shape of a Cruciform Biaxial Tensile Specimen Intended for a Combination of Plane Strain Tensile States

2014 ◽  
Vol 622-623 ◽  
pp. 308-313 ◽  
Author(s):  
Hayato Usui ◽  
Takashi Iizuka
Keyword(s):  
Plane Strain ◽  
Forming Limit Diagram ◽  
Strain Ratio ◽  
Tensile Tests ◽  
Tensile Specimen ◽  
Forming Limit ◽  
Cruciform Specimen ◽  
Minimum Cross Section ◽  
Flat Type ◽  
Width Direction

This study investigates the shape of a cruciform specimen that is stretched in the normal direction of the minimum cross section using FEM. In addition, plane strain tensile states exist in the measurement region in order to determine the forming limit diagram not by an arbitrary stress ratio but by the strain ratio. We propose two types of cruciform specimens. One is a flat-type cruciform specimen, which has deep slits in the middle of the arm region in the width direction. The other specimen is a reduced measurement region type, which also has deep slits as well as a shape that is a biaxial combination of two plane strain tensile specimens. We analyze equibiaxial tensile tests of these two proposed cruciform specimen types using FEM.

scholarly journals Comparative Investigation of the Experimental Determination of AA5086 FLCs under Different Necking Criteria

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3685
Author(s):  
Xiangrui Kong ◽  
Xingrong Chu ◽  
Chongqian Chen ◽  
Yangang Wang ◽  
Peixing Liu ◽  
...  
Keyword(s):  
Forming Limit Diagram ◽  
Comparative Investigation ◽  
Forming Limit ◽  
Forming Limit Curve ◽  
Localized Necking ◽  
Marciniak Test ◽  
Height Change ◽  
Comparative Results ◽  
Nakajima Test

The construction of a forming limit diagram (FLD) is a conventional approach to obtain limit strains and to evaluate the formability of sheet metal. Appropriate necking criteria should be applied to determine the forming limit curve (FLC) accurately. In recent years, deep research on the determination of the FLC has been carried out; meanwhile, several necking criteria have been proposed. However, the application of inappropriate necking criteria would cause deviations when determining FLCs. In this study, both Marciniak and Nakajima tests were carried out on the AA5086 aluminum sheet to make a comparative investigation of different necking criteria in the determination of FLCs. In the Marciniak test, four existing necking criteria were chosen to construct FLCs, and analyzed in detail. The well-performed time dependent and position dependent methods were selected for the Nakajima test. Meanwhile, the modified Wang method based on the height change of the adjacent points was proposed. The comparative results showed that the time and position dependent methods were relatively conservative in both experiments, while the modified Wang method could identify the onset of localized necking more accurately.

Developing Uniaxial Tensile Test as an Alternate Method for Thermo Mechanical Process Evaluation

2011 ◽  
Vol 383-390 ◽  
pp. 5404-5408
Author(s):  
Dedi Priadi ◽  
Richard A. M. Napitupulu ◽  
Eddy S. Siradj
Keyword(s):  
Tensile Test ◽  
Plane Strain ◽  
Testing Machine ◽  
Forming Limit Diagram ◽  
Grain Structure ◽  
Forming Limit ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Mechanical Process ◽  
Uniaxial Test

The alternate method for evaluating the thermo mechanical process has been developed. Small attention has been paid to the mechanism of plastic deformation especially plane strain analysis. Modified the specimen geometry and using uniaxial tensile test was done to view the process. Experimental results show that the forming limit diagram as one of the formability characteristic can be view the plane strain condition that present on the thermo mechanical process. The microstructure result shows that there is a similar grain structure between hot tensile test and hot rolling results as one of thermo mechanical process method. It was concluded that the uniaxial test using universal testing machine could be done to evaluate the thermo mechanical process.

Orientation and formability of orthotropic sheet metals

1997 ◽  
Vol 32 (1) ◽  
pp. 61-81 ◽  
Author(s):  
D W A Ress ◽  
R K Power
Keyword(s):  
Plane Strain ◽  
Principal Stress ◽  
Stress Ratio ◽  
Rolling Direction ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Sheet Metals ◽  
Principal Stresses ◽  
Thickness Strain ◽  
Automotive Sheet

This paper examines the formability of automotive sheet metals: CR steels and 6000 series aluminium-magnesium alloys. Necking strains are used to determine the forming limits; i.e. a diffuse instability condition is reached under in-plane biaxial stressing. The theory admits material anisotropy, work-hardening and sheet orientation under any ratio of applied principal stresses. It has been programmed to accept orientations between the principal stress axes and the sheets' rolling direction in 15° increments between 0° and 90°. The ratio between the principal stresses may vary between 0 and ± 1. The input data required are the width-thickness strain ratios ( r values) in directions 0°, 45° and 90° to the roll and the Hollomon hardening exponent ( n value). The output is presented in four diagrams: the critical subtangent-stress ratio and plots between three combinations of the limiting principal engineering strains: (a) two in-plane strains, (b) major in-plane strain versus thickness strain and (c) minor in-plane strain versus thickness strain. Each diagram shows the influence of rotating the principal stress axes in increments of 15° to the roll. The forming limit diagram of type (a) gives the traditional presentation of a forming limit diagram (FLD). This FLD may be established experimentally from the strain in a surface grid lying around splits. In practice, a few production panels may be gridded for die-tryout and to examine a change in material. The alternative FLDs, types (b) and (c), are proposed to provide quality control with the increasing use of ultrasonics to monitor thickness of pressed panels. An example of type (b) is determined experimentally for CR1 steel.

Optimization of Tube Hydroforming Process Using Probabilistic Constraints on Failure Modes

2011 ◽  
Vol 62 ◽  
pp. 21-35 ◽  
Author(s):  
Anis Ben Abdessalem ◽  
A. El Hami
Keyword(s):  
Failure Modes ◽  
High Reliability ◽  
Thickness Distribution ◽  
Tube Hydroforming ◽  
Forming Limit Diagram ◽  
Plastic Instability ◽  
Probabilistic Constraints ◽  
Forming Limit ◽  
Reliability Based Design ◽  
Hydroforming Process

In metal forming processes, different parameters (Material constants, geometric dimensions, loads …) exhibits unavoidable scatter that lead the process unreliable and unstable. In this paper, we interest particularly in tube hydroforming process (THP). This process consists to apply an inner pressure combined to an axial displacement to manufacture the part. During the manufacturing phase, inappropriate choice of the loading paths can lead to failure. Deterministic approaches are unable to optimize the process with taking into account to the uncertainty. In this work, we introduce the Reliability-Based Design Optimization (RBDO) to optimize the process under probabilistic considerations to ensure a high reliability level and stability during the manufacturing phase and avoid the occurrence of such plastic instability. Taking account of the uncertainty offer to the process a high stability associated with a low probability of failure. The definition of the objective function and the probabilistic constraints takes advantages from the Forming Limit Diagram (FLD) and the Forming Limit Stress Diagram (FLSD) used as a failure criterion to detect the occurrence of wrinkling, severe thinning, and necking. A THP is then introduced as an example to illustrate the proposed approach. The results show the robustness and efficiency of RBDO to improve thickness distribution and minimize the risk of potential failure modes.

Formability Analysis of AA6061 Sheet in T6 Condition

2015 ◽  
Vol 766-767 ◽  
pp. 416-421
Author(s):  
S. Vijayananth ◽  
V. Jayaseelan ◽  
G. Shivasubbramanian
Keyword(s):  
Experimental Method ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Ansys Software ◽  
Limit Curve ◽  
High Corrosion Resistance ◽  
Forming Limit Curve ◽  
Drawing Test ◽  
Deep Drawing Test ◽  
Alloy 6061

Formability of a material is defined as its ability to deform into desired shape without being fracture. There will always be a need for formability tests, a larger number of tests have been used in an effort to measure the formability of sheet materials. Aluminium Alloy 6061 is a magnesium and silicon alloy of aluminium. It is also called as marine material as it has high corrosion resistance to seawater. In this paper Formability test of AA6061 sheet is done by Forming Limit Diagram (FLD) Analysis. FLD or Forming Limit Curve (FLC) for the forming processes of AA6061 sheets is obtained by Experimental method and FEM. Experimental method involves Deep drawing test of the sheet and ANSYS software is used for FEM.

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